This invention relates to a cleaning procedure and, more specifically, to a method of cleaning test probes that are utilized for contacting conductive pads on electronic devices such as integrated circuit chips.
Integrated circuit chips formed on a wafer may each include multiple contact pads. One known technique for testing such integrated circuits utilizes an array of conductive probes mounted in a base member. Such an assembly is commonly called a probe card. The probes are configured to correspond exactly to the arrangement of pads on each chip. In the probe card, electrical connections respectively extend between the probes and terminals to be connected to associated testing equipment. By bringing the probes into electrical contact with the pads, the circuitry embodied in each chip is connected to the associated equipment for testing.
Heretofore, during the course of successively probing integrated circuit chips of the type having aluminum contact pads, it has been observed in practice that the resistance between the probes and the pads becomes in time unacceptably high. This is particularly true if the testing procedure is specified to be carried out at an elevated temperature, say, 85 degrees C.
A typical expedient resorted to for maintaining the probe-to-pad resistance at acceptable levels is to periodically abrade the probe tips against a rough material such as a ceramic or ground glass surface. However, complete reliance on abrasion as a cleaning technique has some disadvantages. For example, exactly reproducible abrasive procedures are difficult to devise. Also, abrading may degrade the planarity of the probe array and, further, may in time mechanically damage the probe tips to the point where they are unusable. In addition, contaminants scraped from the probe tips during abrasion may end up on the shanks of the probes. Moreover, insulating particles from the abrasive surface may adhere to the probes during the cleaning operation. In turn, these contaminants and particles may later become interposed between the probes and the contact pads thereby preventing the establishment of low-resistance paths therebetween.
Another known expedient for cleaning probes involves the use of an etchant solution containing sodium hydroxide. Such an etchant is, however, undesireable because it is highly corrosive. Moreover, sodium is recognized to be one of the worst contaminants for electronic devices and especially for integrated circuits.
Final electrical testing is performed on finished devices in which considerable processing effort has been invested. Even a slight degradation in probe performance can provide incorrect test results. As a consequence, devices that are actually satisfactory may be discarded as being faulty. The economic cost of such erroneous testing is apparent and can be substantial.
In view of the above, efforts have been directed at trying to devise a simple alternative procedure for cleaning test probes utilized to contact aluminum pads on integrated circuit chips. It was recognized that such efforts, if successful, would provide an improved cleaning procedure that would lead to more reliable testing of electronic devices with an attendant reduction in the overall cost of the devices.